A backpack is a means for a person to carry a load.
FIG. 1 illustrates a backpack referred to in U.S. Pat. No. 4,676,418, entitled “Backpack Having Improved Load Distribution and Stabilizing Structures”, by Greg E. Lowe (Lowe). A person has a backpack 100 mounted on his back. The backpack comprises a flexible sack 102 and a sheet frame 104. A shoulder harness 106 and a hip harness 108 are provided to mount the pack on the person. Lowe referred to means whereby the hip harness allows vertical movement 114 of the hips while the person walks 120. The shoulder harness, however, is designed to keep the pack at a fixed position and orientation relative to the person's shoulders. Lift straps 112 are provided to help the person adjust the relative weight distribution between the shoulder harness and the hip harness.
FIGS. 2A and 2B illustrates a backpack suspension referred to in U.S. Pat. No. 5,184,764, entitled “Load Support” by Orovan et al. (Orovan). A hip harness 202 is affixed to a pack frame (not shown) by a mounting plate 204. A shoulder harness 206 is affixed to the hip harness by a slideable webbing means 208. This allows the person wearing the pack to raise and lower his or her arms. When the right arm 200 is up, the right shoulder pad goes up. When the left arm 210 goes up, the webbing 212 slides through a buckle and the left shoulder pad goes up.
The features in the aforementioned back packs are described as suitable for walking or other relatively slow motions carried out by a person wearing a backpack. Hence they are suitable for gaits that merely require freedom of movement. They do not, however, take into account the requirements of a person engaged in relatively rapid gait, such as running. The requirements of running differ from walking due the fact that inertia and elastic energy recovery in the oscillating and twisting motions of the runner are important. A person is bouncing up and down and twisting from side to side as he or she runs. Running efficiently with a pack with substantial weight in it, therefore, requires that the pack be able to respond to the up and down and twisting body movements of the runner without causing undue discomfort or energy loss. Furthermore, the pack must be able to adapt to the changing stance and movements that a person goes through as he or she transitions from walking to running and vice versa.